1. Field of the Invention
Embodiments of the present invention generally relate to well screens and more particularly to inspection of slot thickness between adjacent wraps of wire on wire-wrapped well screens.
2. Description of the Related Art
In the drilling of oil and gas wells, a wellbore is formed in a formation and typically lined with a string of steel pipe commonly referred to as casing. In a process generally referred to as well completion, a string of tubular elements and various pieces of equipment required to enable safe and efficient fluid production are assembled downhole, often within the casing. As part of the well completion process, the casing is typically perforated to allow fluids to flow from an adjacent portion of the formation into the wellbore. In many cases, these formation fluids include undesirable particles, such as sand, that may result in inefficient production if not screened from the production flow.
Producing sand along with well fluids can result in premature failure of production equipment (e.g., artificial lift equipment). Further, collections of sand (sand bridges) formed in the casing or tubulars may impede and eventually obstruct flow of the production fluids. Sand production may also cause erosion or compaction of the surrounding formation which may lead to casing failure. Casing failure in or around a producing zone may lead to loss of the well. Therefore, the control of sand flow from formations is one of the most critical problems in well completion. In some cases, to control sand, a well screen is placed in the wellbore and the surrounding annulus is packed with gravel of a specific size designed to prevent the passage of formation sand into the production flow. The primary objective of this “gravel pack” is to prevent the flow of formation sand, while causing minimal impairment to well productivity.
One type of well screen commonly used for gravel pack applications, as well as stand-alone sand control applications, is a wire-wrapped well screen. A wire-wrapped well screen is typically formed by helically wrapping wire having a controlled profile around a length of perforated base pipe. The thickness of the continuous slot formed between adjacent wraps of the wire is controlled to be small enough to retain the gravel placed behind the screen (or any material to be screened from the production fluid), yet minimize any restriction to flow of the production fluid. Therefore, it is highly desirable that the thickness of this slot (commonly referred to as the slot gauge) be maintained as uniform as possible. Wire-wrapped well screens may be relatively long (often several tens of feet), while the wrapped wire and slot thickness may be relatively small (often less than 0.1 inches and 0.01 inches, respectively). Thus, current processes for manufacturing wire-wrapped well screens yield a product with tens of thousands of slots (i.e., portions of the continuous slot between adjacent wire wraps) to inspect.
Despite the fact that the thickness of slots between adjacent wire wraps may be the most critical attribute of a wire-wrapped screen, the large number of slots makes inspecting each slot economically impractical using conventional measurement techniques. For example, conventional inspection techniques include manually sliding a feeler gauge (e.g., a metal leaf of a known thickness) into the slot or manually using an optical scope to measure slot thickness, both of which are time consuming and prone to human error. To save time, a relatively small set of sample slots may be measured and statistical techniques may be applied to determine an average slot thickness, minimum/maximum slot thickness, and the like. However, the relatively small set of sample slots may be insufficient as there may be relatively long sections of the continuous slot between slot samples that are not inspected.
Accordingly, what is needed is an improved method for inspecting wire-wrapped screens to measure slot thickness between adjacent wire wraps, preferably, an automated system that allows for faster inspection than conventional manual inspection techniques.